Neue Untersuchungsergebnisse �ber den Kreislauf des Kindes unmittelbar nach der Geburt

Color Doppler echocardiographic evaluation of tricuspid regurgitation and systolic pulmonary artery pressure in the full-term and preterm newborn

Color Doppler echocardiography of tricuspid valve regurgitation (TR) is a valid, noninvasive method of determining systolic pulmonary artery pressure (SPAP). In a prospective study the authors examined 56 healthy full-term newborns (group I), 36 healthy preterm newborns (group II), and 10 preterm newborns with severe respiratory distress syndrome requiring surfactant replacement therapy (group III). Doppler studies were repeated until the transtricuspid gradient was < 20 mm Hg. In 83.3% of children a reproducible spectral curve was recorded at least once. The authors estimated the transtricuspid gradient delta p (RV-RA) by using the modified Bernoulli equation. Within the first twenty-four hours delta p (RV-RA) was < 20 mm Hg in 72.7%, 50%, and 25% of children with measurable TR in groups I, II, and III, respectively, increasing to 91.1%, 78.6%, and 55.6% within forty-eight hours. There was no significant correlation between SPAP and gestational age, birth weight, mode of delivery, and ductal closing time. Continuous holosystolic envelope tracing of TR was recorded in 16.6%. In these patients delta p (RV-RA) was measured markedly higher (mean of 30.1 mm Hg) than in the others (mean 17.3 mm Hg). The authors conclude that there is a high prevalence of TR in neonates, which allows estimation of SPAP in > 80% of newborns without considerable impairment. Normalization of SPAP takes place within four days in most patients, but there is a delay in preterm infants with severe respiratory distress syndrome.

Two-dimensional Doppler echocardiographic assessment of closure of the ductus arteriosus in normal newborn infants

To elucidate the mechanism involved in closure of the ductus arteriosus (DA), 50 normal full-term infants were examined with two-dimensional and pulsed Doppler echocardiography. The examinations were performed initially within 1 hour after delivery and serially for 3 days. The two-dimensionally derived long-axis plane of the DA disclosed a characteristic localized protrusion into its lumen in 30% of the subjects within 1 hour, in 80% by 4 hours, in 96% by 8 hours, and in all by 24 hours after birth. In 10 infants in whom the intraluminal protrusion did not appear within 4 hours after birth, none had any recognizable changes in the inner diameter or length of the DA during this initial period. The development of the intraluminal protrusion resulted in localized narrowing of the ductal lumen. Doppler echocardiography revealed a high-velocity jet within and downstream from the narrowed portion of the DA. Thereafter, ductal narrowing progressed along the entire length. The intraluminal protrusion may be early evidence of ductal changes leading to eventual functional and anatomic closure.

Artificial circulation for resuscitation after prolonged clinical death caused by hypoxia

The dynamics of dying and the subsequent recovery of the main vital functions such as cardiac performance, respiration and unconditioned reflexes were investigated in 24 dogs resuscitated by Bryukhonenko's method of artificial circulation after 13-15 min clinical death caused by asphyxia. Application of artificial circulation during asystole required a gradual increase for 2-3 min in the volume of perfusion to optimum levels, since too rapid an increase of blood flow resulted in secondary ventricular fibrillation. In conditions of resuscitation with high volumes of extracorporeal perfusion (exceeding 100 ml kg-1 min-1), fast return of vital functions, their subsequent normalization, and relatively smooth recovery, can be achieved. Decreasing the rate of blood flow to 60-80 ml kg-1 min-1 delays the recovery of vital functions of the resuscitated organism. Severe post-resuscitation disease develops with a fatal outcome. Resuscitation with flows of 40 ml kg-1 min-1 or less is ineffective. We concluded that successful resuscitation after clinical death caused by asphyxia was possible only when the blood flow was 1.2-1.5 times higher than the normal cardiac output.

The influence of different environmental temperatures on pulmonary gas exchange and blood gas changes after birth

The oxygen uptake (VO2) and respiratory exchange ratio (R) was determined during the first 20 min and at one and at 2 hours after birth in 16 healthy full-term newborn infants studied in different environmental temperatures. Arterial blood gases and acid-base balance were determined on repeated blood samples from the abdominal aorta. The infants were grouped in a "warm" group (n equal to 10) where efforts were made to avoid cooling after birth, and a "cold" group (n equal to 6) where a decrease in rectal temperature to a mean value of 35.4 degrees C at 2 hours occurred. Irrespective of environmental temperature, VO2 was approximately 10 ml/kg min during the first 8 min after birth, thereafter decreasing to about 6-7 ml/kg min. During the first 8 min the main increase in PaO2 occurred and about 2 ml/kg min of the VO2 was accounted for by changes in oxygen stores after birth. At 16-20 min and at 60 min after birth a negative relationship was found between VO2 and PaO2. During the period 8-120 min after birth a close relationship was found between VO2 and the degree of muscular activity. Within 4-16 min after birth, R values above 1.0 were regularly found simultaneously with the main decrease in PaO2. In infants kept "cold" a tendency to hyperventilate was found, probably elicited by cold stimuli. The rapid drop in deep body temperature regularly seen after birth could thus not be explained by a limited ability to increase pulmonary gas exchange. A high degree of evaporative heat loss, a relatively low "basal" metabolic rate and a limited response in "non-shivering thermogenesis" seem to be the main reasons for the heat loss after birth.

Transposition of the great arteries. Changes in the circulation after birth

Sequential cardiac catheterizations were performed on 19 infants with complete transposition of the great arteries (TGA). None had any additional cardiac abnormalities other than an atrial septal defect. All were under 3 months of age at the time of the initial study. The pulmonary artery pressures and pulmonary-to-systemic vascular resistance ratios were significantly higher under the age of 9 weeks than over this age. The major fall in pulmonary vascular resistance appeared to occur in the first 4 weeks of life. A systolic pressure gradient from the left ventricle to the pulmonary artery of more than 5 mm Hg (median 13) was found at all the investigations performed in patients over the age of 2 weeks. This suggests that such a pressure gradient is usual in TGA, and not a sign of pulmonary stenosis. No systematic distribution of pulmonary-to-systemic flow ratios or age-related changes in these ratios was demonstrated, but pulmonary flow was rarely the same as systemic flow. In TGA the pulmonary vasculature undergoes a maturation process with the transition from intra- to extrauterine life. This process is similar in magnitude and time scale to that seen in the normal human infant.